Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$18.52	9.702%	$20.3168	$20.32	$20.30	$20.30
Purchase #2	$63.76	5.271%	$67.1208	$67.12	$67.10	$67.10
Purchase #3	$205.63	11.856%	$230.0095	$230.01	$230.00	$230.00
Purchase #4	$209.98	11.348%	$233.8085	$233.81	$233.80	$233.80
Purchase #5	$228.76	9.165%	$249.7259	$249.73	$249.75	$249.70
Purchase #6	$65.49	10.522%	$72.3809	$72.38	$72.40	$72.40
Purchase #7	$250.91	12.627%	$282.5924	$282.59	$282.60	$282.60
7 purchase totals =	$1,043.05		$1,155.9548	$1,155.96	$1,155.95	$1,155.90